The present invention generally relates to sensors and, more specifically, to a pressure sensor, accelerometer or the like that is resistant to damage from freezing.
Various types of pressure sensors are generally known to those skilled in the art. One type of pressure sensing device comprises a silicon die that is etched to form a cavity in a surface of the die. The etched cavity does not extend entirely through the thickness of the die but, instead, a diaphragm portion is left remaining in the opposite surface of the silicon substrate. The diaphragm portion is sufficiently thin to flex in response to differences in pressure on its upper and lower surfaces. In a manner that is well known to those skilled in the art, stress sensitive components can be disposed on the upper surface of the diaphragm portion formed over the cavity. When the diaphragm portion flexes in response to pressure exerted on it, the stress sensitive components provide a means for detecting the flexing of the diaphragm portion. It is common for piezoresistors to be used as the stress sensing components.
In order to achieve miniaturization, an electronic circuit can be disposed on a common surface of the pressure sensor die with the stress sensing components. In addition, electrically conductive pads can be deposited on the same surface of the pressure sensor die in order to facilitate the connection of the die to external devices. The pressure sensor die is commonly made of silicon. In addition, it can be attached to a silicon or glass substrate which provides stress isolation between the diaphragm portion of the die and external components, such as fluid conduits, which are typically used to conduct a flow of a fluid to the cavity portion of the die or to the portion above the diaphragm portion of the die. Silicon pressure transducers of this general type can be used to measure either absolute pressure or differential pressure.
Pressure sensing devices of the above type are susceptible to damage due to freezing. During operation, it will be appreciated that the silicon die has a temperature that is elevated relative to the surrounding area. When operations subsequently cease, the die gradually cools to ambient temperature, thereby creating a slight vacuum in the cavity. Simultaneously, the cooling silicon die creates condensation, and the vacuum in the cavity tends to pull the condensation into the cavity. When the ambient temperature drops below freezing, the volume of condensation expands as it forms ice, thereby potentially damaging the die and buffer.
U.S. Pat. No. 5,412,994, which issued to Cook et al. on May 9, 1995, discloses an offset pressure sensor in which the pressure sensing components are isolated from a portion of an attached buffer member which is connected to a fluid conduit. The buffer has an opening, while the sensor die has a cavity defining a diaphragm, the cavity being offset from the opening. The opening and the cavity are placed in fluid communication by a relatively large channel formed in the glass buffer. The pressure sensor may also include elastomeric conductors and pressure seals to eliminate the need for making solder connections between the sensor structure and external components. The offset layout and elastomeric conductors isolate stresses transmitted between an attached external fluid conduit and sensitive components of the pressure sensor.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
In accordance with certain aspects of the present invention, a sensor is provided comprising a buffer member having upper and lower surfaces and defining an opening extending from the upper surface to the lower surface. A pressure sensor die has a first surface and a second surface attached to the upper surface of the buffer member. The pressure sensor die further has a diaphragm portion of the first surface extending across a cavity formed in the second surface of the pressure sensor die. A capillary channel has a first end in fluid communication with the cavity and a second end in fluid communication with the opening of the buffer member, the capillary channel having a cross-sectional area sized to resist liquid flow therethrough. The diaphragm portion functions as a pressure sensing component, and a first fluid conduit is disposed in fluid communication with the opening of the buffer member.
In accordance with additional aspects of the present invention, a pressure sensor is provided having freeze resistant characteristics. The pressure sensor comprises a glass buffer member having upper and lower surfaces and an opening extending from the upper to the lower surface. A silicon die has an upper surface and a lower surface adapted for attachment to the upper surface of the buffer member, a cavity formed in the lower surface of the silicon die defining a flexible diaphragm portion of the silicon die, and a capillary channel formed in the lower surface of the silicon die extending from the cavity to an inlet portion of the silicon die located adjacent the opening to establish fluid communication between the opening and the cavity. The diaphragm portion functions as a pressure sensing component.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.